It's interesting how much Sidious' betrayal of Maul is a matter of perspective
Like I'm not trying to defend Sidious here, but from the way Maul (and the Maul stans) talk about it, you'd think Sidious intended all along to get rid of Maul, that it was all a plan, that Sidious deliberately sent Maul to Naboo with the hope that he'd die, that Sidious backstabbed Maul or kicked him aside in Phantom Menace
He didn't, Maul's defeat and presumed death was not part of the plan, this was a genuine loss for Sidious, he was not counting on this, and speaking of presumed death, that's another important detail, Sidious really thought Maul was dead, he took Dooku on as his new apprentice under the very reasonable assumption that Maul was truly dead and gone, this wasn't a case of "you failed me so I'm replacing you with someone better", this was "my best agent is dead (as far as I or anyone else is aware) and I need someone who can pick up the slack", and based off the fact that Sidious did take the time to rescue and rebuild Vader despite the latter's horrific injuries, Sidious probably would have repaired Maul and kept him as his apprentice (until someone who was better came along) had Maul managed to make it back to Sidious quickly enough
Really it's only after Maul comes back, after Dooku has been Sidious' apprentice for 12 years, and the plan is in the final stages, nearing it's culmination, (and while Maul is working independently to undermine Sidious and has taken on his own apprentice, creating a violation of the rule of two and de facto starting a sith civil war) that Sidious outright declares to Maul "you are replaced, I no longer need you"
What's my point in all this? Well like I said, not trying to defend Sidious, I think this all says more about Maul than it does Sidious
Sith Apprentice dies (or seems to die)? Their Master finds a new one. That's standard procedure for the sith, even before the rule of two, Maul would have known this from sith history and the tutelage he received from Sidious
Maul almost seems to have this... expectation that Sidious and the sith's grand thousand year plan was going to wait for him, that it would have been put on hold for his sake, that he was special, important, an exception, or unique in the sith's grand design, that he was one of a kind among sith, better than all that came before, unmatched by any that would follow
In other words, a very typical sith belief in self importance, arrogant and egotistical in their view of themselves in the galaxy
